Average current and frequency control

ABSTRACT

Apparatuses, systems and methods for regulating the output currents of a power supply at a target output current include a buck converter module operably connected to a power source and a load. A first switch couples the power source to the buck converter module during a first period of a given operating cycle, while the buck converter module stores and provides electrical power to the load. During a second period, a second switch may discharge, the electrical power stored during the first period. A current sensor senses the currents during at least one of the first period and the second period and, over the operating cycle, the switching times are adjusted so the average output current equals the target output current. Adjustments to the first and second period durations result in maximum and a minimum currents symmetrically disposed about the average current provided to the load during the operating cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Utility application Ser.No. 15/378,517 (the “'517 application”), filed on Dec. 14, 2016, and toU.S. Provisional Application Ser. No. 62/410,937 (the “'937application”), filed on Oct. 21, 2016 each of which are entitled“Apparatus, Systems and Methods for Average Current and FrequencyControl in a Synchronous Buck DC/DC LED Driver,” and were filed in thename of inventor Jean-Paul Eggermont, the entire contents of each of the'517 application and the '937 application are incorporated herein byreference.

TECHNICAL FIELD

The technology described herein generally relates apparatus, systems andmethods for regulating currents produced by buck converters. Thetechnology may find use in electronic devices, such aslight-emitting-diode (LED) lighting applications and in otherapplications where control of the average currents used to drive LEDunits and similar types of loads is desired.

BACKGROUND

Today, LED lighting is gaining wide-spread acceptance in automotive,industrial and other lighting applications. As is commonly known andappreciated, LED lighting generally requires less energy to produce adesired quantity of light, where the quantity of light is oftenexpressed in lumens and along a correlated color temperature range,often expressed in degrees Kelvin. In some LED applications, such asautomobile front head-light applications, relatively high LED voltages,often ranging between 4 to 50 Volts, and high currents, often rangingfrom 100 mAmps to 3 Amps, are commonly used. Such LED systems arecommonly used to produce a range of Lumens over a given range at a colortemperature in degrees Kelvin that is not noticeably perceptible by adriver. The quantity and temperature range of light produced, however,may vary based upon operating, user preference and other considerations.It is to be appreciated that the light produced by LED units is commonlyproportional to the current used to drive the LED units. Given thesevoltage, current, lumen and temperature ranges, the regulation of thecurrent flowing through the LEDs is very important.

As shown in FIG. 1, one common circuit 100 used today to regulate thecurrent flowing through high power LED units utilize circuits thatinclude a similar power source 102, connected to a DC/DC buck convertermodule 104. The buck converter module 104 commonly includes coils andcapacitor which facilitate the storage and discharge of electricalenergy, these inherent capabilities buck convertors are referred toherein as providing an energy storage module. Often the buck convertermodule 104 and related switching components are provided in a commonballast 106, but, may be provided separately or as components of largersystems or units. The principles of operation and elements of such buckconverter module 104 are well known in the art and are not describedherein but are incorporated herein by reference and by inherency. It isto be appreciated that one or more of the components of the buckconverter module and/or the switch 116 shown in FIG. 1 may be replacedand/or augmented by other known circuit components and configurations.For example, diode 126 could be replaced by a N-type field effecttransistor (FET) for a synchronous converter.

Further, it is to be appreciated that the electrical characteristics ofone or more of the components of a buck converter, as shown for examplein FIG. 1 and in FIG. 3 are illustrative only and can be considered tobe elements of other components of the embodiments shown. For example,diode 126 can be considered to be a parasitic diode of switch 306 (asshown in FIG. 3). As is commonly known, the output power, as commonlyexpressed in terms of an LED current I_(LED) and an LED voltage V_(LED),of the buck converter module 104 provides electrical power to one ormore LED units 108 a,b,c-108 n. The LED units 108 a,b,c-108 n may bedriven individually, collectively or some combination in-between by apixel driver module 110 or a similar module (if any). The pixel drivermodule 110 may be used to control whether any given LED unit 108 a-n ispowered or short-circuited, at any given time, by selectivelyopening/closing irrespectively one or more switches 112. Often the pixeldriver module 110 adjusts the opening/closing of the one or moreswitches 112 in accordance with then desired lighting conditions, as maybe sensed, selected or determined based upon ambient light sensors,speed, user preferences, in accordance with regulations and otherconsiderations.

Often a first switch 116, such as an N-channel or P-channel MOSFETtransistor, is used to control the operating state, “on” or “off”, ofthe buck converter module 104. The peak current I_(MAX) of the currentI_(LED) generated through the buck converter module 104 through switch116, and thereby to the LED units 108 a-n, may be sensed at the outputof the buck converter module 104 using, for example, a resistive element118 and an operational amplifier 120. In other embodiments, other formsof current sensing devices and/or module are often utilized. The voltageacross the resistive element 118, as sensed by the operationalamplifier, reflects the peak current I_(MAX) provided to the LED units108 a-n at any given time. By controlling the respective “on” and “off”times of the first switch 116, the currents I_(LED) provided to the LEDunits 108 a-n may be regulated.

As shown, buck converter module 104 commonly includes a coil 122 havingan inductance L. In high current LED applications and in view ofeconomic, design and other considerations, it is often desirable toreduce the inductance L of the coil 122 and eliminate the need for anyexternal sensing elements such as resistive elements 118 which commonlydrain to much power, are expensive, utilize too much physical space onelectrical circuit boards and in view of other constraints.

Ideally, a low cost, low inductance system is needed which enables oneto regulate the average currents provided to the LED units by the buckconverter module 104. These competing desires of low cost, lowinductance coils, exclusion of external sensing elements and others,while maintaining a desired average current and power provided to theLED units, with varying voltage demands of such LED units often arefurther constrained in that a reduction of the coil 122 inductance Loften requires an increase in the frequency at which the coil 122 isswitched “on” and “off.” It is to be appreciated that as the inductanceL of coil 122 decreases, the switching frequency of the coil 122 mustincrease in order to maintain a desired average current and acceptableripple current provided to the LED units 108 a-n.

Further constraining the above considerations and concerns is the needto avoid the generation of undesired electro-magnetic emissions duringoperation. It is commonly known that buck converters generateElectro-Magnetic Radiation (EMRs). High EMRs can influence theoperations of other circuits and components in automobile and otherimplementations of high power LED units. Accordingly, theElectro-Magnetic Compatibility (EMC) of LED driver units is often highlyregulated, especially in motor vehicles. Commonly, EMC concerns limitthe permissible frequency range of buck converter modules to 2 MHz±5%.As such, today a need exists to regulate not only the average currentbut also the switching frequency of LED driver units.

As shown in FIG. 2, today's known circuits (such as the exemplarycircuit shown in FIG. 1) commonly attempt to regulate high power LEDmodules by generating a ripple current R, where the ripple ΔIR of theLED current, I_(LED) is controlled, over time, by the switching of thefirst switch 116 “on” and “off.” These times are shown in FIG. 2 byt_(on) and t_(off). This successive switching produces an average ripplecurrent ΔIR_(avg).

In FIG. 2, the “on” time for the first switch 116 is shown by t_(on).The “off” time for the first switch 116 is shown by t_(off), which isproportional to the voltage V_(LED) provided to the LED units 108 a-n.That is, for these module designs, it is commonly appreciated that thetime off, t_(off) depends on the voltage, V_(LED) of the LED units 108a-n. That is, as V_(LED) increases, t_(off) needs to decrease tomaintain a constant current ripple ΔIR_(avg), and vice versa. Thisrelationship can be expressed mathematically, where L is the value ofthe coil 122 of the buck converter 104, as follows:(toff×VLED)/L=ΔIR.

It is to be appreciated that, per these prior art approaches, theswitching frequency is not controlled, and adjustments are continuallyneeded to prevent the peak current of I_(LED) from continually varyingin response to variations in the input voltages V_(IN) to the buckconverter 104, the properties of the coil 122, and the voltage needsV_(LED) of the LED units 108 a-n, where V_(LED) may vary over time basedupon the variations in the number of LED units on and off at any giventime and the power needs of such LED units.

Further, it is to be appreciated that such designs require theinductance L of the coil 122 to be known and/or the system to becalibrated (and re-calibrated) to such inductance. The inductance of acoil may also vary over time and in response to operating conditions.Further, such commonly known approaches provide only a partial solution,as they still require the inductance L of the coil 122 to be closelymatched to input voltages and loads in order provide a desired V_(LED).As such, commonly available approaches today do not permit a driversystem to be adaptive to varying inductance/coil values of the buckconverter, to variations in the V_(LED) needed at any given time, or tovariations in the input voltage V_(IN).

Therefore, an apparatus, system and method is needed for a controllingthe average currency of a high-powered DCDC LED driver modules andthereby facilitate the use of low inductance coils, and buck convertermodules which can operate independent of the inductance of any givencoil used for a particular implementation, the input voltage, andvarying load conditions while maintaining the switching frequency of thebuck converter module within desired parameters so as to meet EMCcompliance requirements, while also minimizing switching power losses.Such an apparatus, system and method desirably facilitates a synchronousmode of operation, using integrated Field Effect Transistors (FETs),while also being compatible for use with external FETs to provide anasynchronous mode of operation.

SUMMARY

In accordance with at least one embodiment of the present disclosure anapparatus, system, or method for powering an electrical load, such asone or more LED units, includes as it components or in conjunction withone more of its operations, a driver module and a regulating module. Thedriver module may include a buck converter module that is operablyconnected to an electrical load. The buck converter module may includeat least one energy storage module. The driver module may also beconfigured to include a first switch configured to operably couple apower source to the buck converter module during a first operating stateoccurring over a first time period. A second switch may also be providedand configured to operably couple the buck converter module to theelectrical load during a second operating state occurring over a secondtime period. During an operating cycle encompassing both the firstoperating state and the second operating state, a first current sensormay be configured to sense the electrical current provided to theelectrical load while the apparatus is operating in the first state andoutput a first current sensed signal. A second current sensor may beconfigured to sense the electrical current provided to the electricalload while the apparatus is operating during the second state and outputa second current sensed signal. A regulating module may be configured tobe operable to instruct and regulate the time periods during which eachof the first switch and the second switch are configured into at leastone of the first operating state and the second operating state suchthat a maximum current and a minimum current are provided by a buckconverter module to the load over a given cycle and such maximum andminimum currents are symmetrically disposed about an average currentprovided to the load during the operating cycle.

In accordance with at least one embodiment of the present disclosure,the first operating state occurs during a first “on” time period, whilethe second operating state occurs during a second “off” time period. Itis to be appreciated that an operating cycle for the buck convertermodule includes the combination of a given “on” time period with animmediately succeeding “off” time period. It is further to beappreciated that during the first operating state, the buck convertermodule may be configured to provide power to the electrical load andstores power in the electrical storage module. Further, during thesecond operating state, the power stored by the energy storage moduleduring the first operating state may be discharged to the electricalload. Further, during the first time period the regulating module may beconfigured to instruct the first switch to close and substantiallysimultaneously therewith instruct the second switch to open. Inaccordance with at least one embodiment, during the second time periodthe regulating module may be configured to instruct the first switch toopen and substantially simultaneously instructs the second switch toclose.

In accordance with at least one embodiment of the present disclosure, anapparatus, system or method for powering an electrical load may includethe use of a regulating module, which regulates a maximum currentprovided by a buck converter module to a load during the first timeperiod. The regulating module and operations thereof may also beconfigured to regulate a minimum current provided by the buck convertermodule to the load during a second time period. Further, by regulatingthe maximum and minimum currents provided, the regulating moduleregulates the average current at a target current for the load for agiven operating cycle of a DCDC buck converter. In accordance with atleast one embodiment, the regulating module may be configured to includea first comparator module coupled to a second current sensor andconfigured to detect when the minimum current provided to the loadreaches a target minimum current. Per at least one embodiment, when thetarget minimum current is detected, a set signal may be outputted. Theregulating module may also include a period compare module, coupled tothe at least one comparator module, and configured to measure, uponreceipt of the set signal, an amount of time required for the minimumcurrent provided to the load to reach the target minimum current. Per atleast one embodiment, the period compare module may be configured tocompare for each of a first cycle and a second cycle the time when theminimum current provided to the load reaches the target minimum currentfor that cycle and output a result of the comparison.

In accordance with at least one embodiment, a regulating module may beconfigured to include an adjustment module. The adjustment module may becoupled to a period compare module and configured to receive and inversethe outputs of the period compare module. Per at least one embodiment,the inverse of the result of the outputs from the period compare moduleindicate a switching frequency of a driver module. Based on a comparisonof the switching frequency of a current cycle to a target switchingfrequency, an output signal may be generated as a current adjustmentsignal. Per at least one embodiment, the current adjustment signal mayindicate an amount of change desired in the current to be provided tothe load during the next cycle.

In accordance with at least one embodiment, a regulating module may beconfigured to include at least one summing module. The summing modulemay be coupled to an adjustment module and configured to receive atarget current signal and modify the target current signal based on thecurrent adjustment signal generated by the frequency adjustment module.The summing module may also be configured to produce a desired minimumcurrent for the load for a next operating cycle by subtracting thecurrent adjustment signal from the target current. Per at least oneembodiment, the regulating module may also include a second comparatormodule, coupled to a first current sensor, and configured to detect whena maximum current provided to a load reaches a target maximum currentand, when such detection occurs, output a reset signal. Per at least oneembodiment, the second comparator module may be configured to detectwhen the maximum current reaches the target maximum current by comparinga first current sensed signals received by the second comparator modulefor a then arising operating cycle against a desired maximum current forthe next operating cycle. Per at least one embodiment, the desiredmaximum current may be provided to the second comparator module by asumming module and the desired maximum current is the result of theaddition of the current adjustment signal for the present operatingcycle to the target current. Per at least one embodiment, adetermination of a desired maximum current may occur during an operatingcycle occurring immediately previous to the current operating cycle.

In accordance with at least one embodiment of the present disclosure, anapparatus, system or method for powering an electrical load may includethe use of a regulating module, wherein a first current sensor and thesecond current sensor are combined into a joint current sensorconfigured to detect the current provide to the load during each of thefirst operating state and the second operating states. Per at least oneembodiment, the regulating module may include a first comparator moduleand a second comparator module that are combined into a joint comparatormodule. Per at least one embodiment, at least one summing module may beincluded and configured to add a current adjustment signal to a targetcurrent during a first operating state so as to provide a desiredmaximum current for a next operating cycle. Per at least one embodiment,at least one summing module may be configured to subtract a currentadjustment signal from a target current during a second operating stateto provide a desired minimum current for a next operating cycle. Per atleast one embodiment, the regulating module may include a multiplexer,coupled to at least one summing module, and configured to provide to ajoint comparator module, for use during a next operating cycle, adesired maximum current to be reached during a first operating state anda desired minimum current to be reached during a second operating state.

In accordance with at least one embodiment of the present disclosure, anapparatus, system and method for powering an electrical load is providedand may include a driver module. The drive module may be configured toinclude a buck converter module. The buck converter module may beoperably connected to an electrical load, such as one or more LED units.The buck converter module may be a DCDC buck converter and may includeat least one energy storage module, such as one provided by aninductive-capacitive circuit. The drive module may also be configured toinclude, for at least one embodiment, a first switch configured tooperably couple a power source to the buck converter module during afirst operating state. The first operating state may occur over a firsttime period. The drive module may be configured to include, for at leastone embodiment, a second switch configured to operably couple the buckconverter module to the electrical load during a second operating state.The second operating state may occur over a second time period whichfollows a first time period. An operating cycle for the buck convertermay include both the first operating state and the second operatingstate, such that the first operating state occurs during a first “on”time period and the second operating state occurs during a second “off”time period. Per at least one embodiment, an operating cycle for thebuck converter module may include a combination of a given “on” timeperiod with an immediately succeeding “off” time period.

Per at least one embodiment, a first current sensor configured to sensethe electrical current provided to the electrical load while theapparatus is operating in the first state and output a first currentsensed signal may be included. Likewise, a second current sensorconfigured to sense the electrical current provided to the electricalload while the apparatus is operating in the second state and output asecond current sensed signal may be included.

A regulating module, per at least one embodiment, may include a firstcomparator module coupled to a second current sensor and configured todetect when a minimum current provided to a load reaches a targetminimum current and, when such detection occurs, output a set signal.Per at least one embodiment, a period compare module may be included inthe regulating module. The period compare module may be coupled to atleast one comparator module and configured to measure an amount of timerequired for a minimum current provided to a load to reach a targetminimum current.

Per at least one embodiment, a regulating module may be configured toinstruct and regulate one or more time periods during which each of afirst switch and a second switch are configured into at least one of afirst operating state and a second operating state such that a maximumcurrent and a minimum current provided by a buck converter module to theload over a given cycle are symmetrically disposed about an averagecurrent provided to the load during that same operating cycle.

In accordance with at least one embodiment of the present disclosure anapparatus for regulating the currents provided by a DCDC buck convertersto an LED unit, may be configured to include a regulating moduleoperable to instruct and regulate the time periods during which each ofa first switch and a second switch of a driver module are configuredinto at least one of the first operating state and a second operatingstate such that a maximum current and a minimum current are provided bya buck converter module to an LED unit over a given operating cycle aresymmetrically disposed about an average current provided to the LED unitduring the given operating cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, advantages, functions, modules and components ofthe apparatus, systems and methods provided by the various embodimentsof the present disclosure are further disclosed herein with regard to atleast one of the following descriptions and accompanying drawingfigures.

FIG. 1 is schematic representation of a prior art approach to regulatingthe operation of buck converters driving LED units.

FIG. 2 is a timing diagram illustrating the resulting ripple currentthat may be produced in conjunction with the use of the prior artapproach of FIG. 1.

FIG. 3 is a schematic diagram illustrating an apparatus, a drivermodule, for use in regulating the operation of a buck converter module,by regulating the average current produced by the buck converter module,in accordance with at least one embodiment of the present disclosure.

FIG. 4A is a timing diagram illustrating the principles of operation ofa first, “hi” switch used in the apparatus of FIG. 3 and in accordancewith at least one embodiment of the present disclosure.

FIG. 4B is a timing diagram illustrating the principles of operation ofa second, “low” switch used in the apparatus of FIG. 3, and inaccordance with at least one embodiment of the present disclosure.

FIG. 4C is a timing diagram illustrating the regulation of the averagecurrent provided by a buck driver module to at least one LED unit, asthe operation of such buck driver module is regulated per the apparatusof FIG. 3 and in accordance with at least one embodiment of the presentdisclosure.

FIG. 5 is a schematic diagram illustrating an apparatus, a regulatingmodule, for use in controlling the principles of operation of the drivermodule of FIG. 3, in accordance with at least one embodiment of thepresent disclosure.

FIG. 6 is a schematic diagram illustrating an apparatus, a secondregulating module, for use in controlling the principles of operation ofthe driver module of FIG. 3, in accordance with at least one embodimentof the present disclosure

DETAILED DESCRIPTION

The various embodiments described herein are directed to apparatus,systems and methods by which the average current of a direct current(DC) buck converter module may be regulated. While the variousembodiments set forth herein, and as shown in the attached drawingfigures, provide sufficient information for a person of ordinary skillin the art to practice one or more of the inventions, as claimed hereinor as later claimed in any application claiming priority to thisdisclosure, it is to be appreciated that one or more embodiments may bepracticed without one or more of the details provided herein. As such,the various embodiments described herein are provided by way of exampleand are not intended and should not be used to limit the scope of anyinvention claimed to any particular embodiment.

As shown in FIG. 3 and for at least one embodiment of the presentdisclosure, a driver module 300 is provided for sensing and regulatingthe current, I_(LED), provided to one or more LED units 108 a-n. Drivermodule 300 may include a DCDC buck converter module 104.

It is to be appreciated, that current I_(LED) will vary over time and isthe same as the current produced by buck converter module 104 at anygiven time. Buck converter module 104 includes a coil 122 having aninductance L, a capacitor 124 having a capacitance C₁, and at least one“high” switch 304 and one diode 313. It is to be appreciated that for atleast one embodiment of the present disclosure, the sensing andregulating of current I_(LED) is independent of the inductance andcapacitances used for any given implementation. The inductance andcapacitance values being used for the DCDC buck converter module 104 maybe selected by a person of ordinary skill in the art based uponwell-known electrical circuit design principles which are incorporatedherein by reference and by inherency.

Driver module 300 may be configured to include two switches, “hi” switch304 and “low” switch 306, which are used to control the “on” and “off”cycles of buck converter module 104. In accordance with at least oneembodiment, switches 304 and 306 may be MOSFET transistors. In FIG. 3,elements 312 and 313 respectively represent the parasitic capacitanceand parasitic diode properties of low switch 306. In other embodiments,other type of transistor or other switches may be utilized. The currentI_(SW1) across “hi” switch 304 and the current I_(SW2) across “low”switch 306 are sensed during their respective “on” times by respectivehi current sensor module 314 and low current sensor module 316. Anyknown devices, modules, techniques or otherwise may be used to monitorthe currents flowing across the respective hi switch 304 and low switch306 during the respective states of operation of the driver module 300.One example of such known current sensing devices is the user of asensing resistor. Further, it is to be appreciated that internal currentsensing on one or both of the hi switch 304 and the low switch 306 maybe used in one or more embodiments of the present disclosure.

As further shown in FIG. 3 and as additionally shown in FIG. 5, “hi”lead 308 and “low” lead 310 couple driver module 300 with regulatingmodule 500. At least one embodiment of regulating module 500 isdescribed below and shown in FIG. 5. Leads 308 and 310 respectivelycommunicate signals I_(sense1) and I_(sense2) representative of currentsI_(SW1) and I_(SW2), from driver module 300 to regulating module 500.

As further shown for at least the embodiment illustrated in FIG. 5,driver module 300 receives power V_(in) from a source 102 (not shown inFIG. 3) or another power source. It is to be appreciated that drivermodule 300 may receive power from any source configured to provide thedesired voltage or voltage ranges. Such power sources are well-known inthe art and are incorporated herein by reference and inherency. Inaccordance with at least one embodiment of the present disclosure,V_(in)=12 volts DC and V_(LED)=10 volts DC may be possible values.

The principles of operation of driver module 300 are shown in FIGS. 4A,4B and 4C, where FIG. 4A shows the characteristics of current I_(SW1),FIG. 4B shows the characteristics of current I_(SW2), and FIG. 4C showsthe resulting I_(LED) current provided to the LED units by the buckconverter module 104. More specifically, in FIGS. 4A, 4B and 4C, thosetime periods when the buck converter module 104 is considered “on” and“off” are respectively shown as times t_(ON) and t_(OFF). In accordancewith the present naming convention, t_(ON) represents time period t1_(n) to t3 _(n), where n is an integer and represents a given cycle ofoperation of the buck converter module, where a single cycle includesthe time period occurring from when the buck converter module isswitched into an “on” state, then to an “off” state and then toimmediately prior to it returning to an “on” state). More specifically,when hi switch 304 is “closed” and low switch 306 is “open”, the buckconverter module is considered to be in the “on” state. Contrarily,t_(OFF) represents the time period from t3 _(n) to t5 _(n), where t5_(n)=t1 _((n+1)) and t5 _(n) and t1 _((n+1)) both represent thebeginning of the next cycle for the buck converter module 104. That ist_(OFF) occurs when hi switch 304 is open and low switch 306 is closed.It is to be appreciated that for at least one embodiment, the operatingstates (on/off) of hi switch 304 and low switch 306 are diametricallyopposed. In accordance with other embodiments, some delay and overlap inrespective “on” and “off” times may occur between the irrespective “on”and “off” states of the hi and low switches 304 and 306 respectively.For purposes of this disclosure, such delays, when arising in theNano-Second range of 1 ηSec. to 10 ηSec. are considered to beinsubstantial, such that for all practical purposes the switching “on”and “off” (and the inverse operations thereof) of the hi switch 304 andthe low switches 306 res are considered to occur substantiallysimultaneously.

In at least one embodiment, time t3 _(n), which as shown in FIG. 4A isthe beginning of the t_(OFF) period, is determined to occur when theI_(sense1) current reaches I_(MAX). Similarly, for at least oneembodiment, time t5 _(n)=(t1 _((n+1))) is determined to occur when theI_(sense2) current reaches I_(MIN). It is to be appreciated that byadjusting the values of I_(MAX) and I_(MIN) the time periods t3 _(n),and t5 _(n)(t1 _((n+1))) are obtained. By adjusting the values I_(MAX)and I_(MIN), symmetry of I_(MAX) and I_(MIN) relative to a desiredtarget current I_(TAR) the resulting average current I_(AVG) can beobtained and equaling a desired target current I_(TAR), where the targetcurrent is the desired operating current for the LED units 108 a-n. Itis to be appreciated that I_(TAR) may be pre-determined, specified inadvance, determined experimentally, calibrated once or repeatedly or maybe otherwise identified for use in accordance with a given one or moreLED units 108 a-n. It is to be further appreciated that the value ofI_(TAR) may vary in accordance with the principles of operations used inconjunction with a given (if any) pixel driver module 110 used inconjunction with one or more embodiments of the present disclosure.

As shown in FIG. 4A for at least one embodiment of the presentdisclosure, time tc represents the time period t1 _(n) to t2 _(n) usedto charge the parasitic and/or additional capacitance C₂ of the buckconverter module 304. As discussed above, such parasitic capacitance, asrepresented by element 312, may arise, for example, in association withthe activation of the hi switch 304 itself, or otherwise. As shown,during the charging of second capacitance, current I_(SW1) through hiswitch 304 initially has a peak current I_(C2). For at least oneembodiment, current I_(SW1) sensed during time period tc may be maskedand is not used to regulate the average current provided by drivermodule 300 to LED units 108 a-n. After time period tc current I_(SW1)may be sensed and generally increases from a value I_(SW1Min) to themaximum current I_(MAX) provided by driver module 104 to the LED units108 a-n. Accordingly, the currents sensed I_(SENSE1) and used byregulating module 500 to regulate the operation of driver module 300 maybe expressed mathematically, for any given cycle n, as shown in Equation1.I _(SENSE1) =Isw1  Equation 1:Per Equation 1, for any given cycle n, t2 _(n) is the time from when thecurrent sensed by high current sensor 314 is representative of the coilcurrent while the hi switch 304 is “on”, and t3 _(n) is the time atwhich the hi switch 304 is turned “off.”

As shown in FIG. 4B for at least one embodiment of the presentdisclosure, after the hi switch 304 is turned off at time t3 _(n), lowswitch 306 is turned on and diode 126 reverses the node of the buckconverter 104 to the low switch 306. At the beginning of the “off” timet_(OFF), at time t3 _(n), the sensed current I_(SW2) flowing through lowswitch 306 initially presents itself as a recovery current induced bydiode 126. The recovery current generally occurs over time period t3_(n) to t4 _(n), which is represented in FIG. 4B by time period td. Forat least one embodiment, current I_(SW2) sensed during time period tdmay be masked and may not be sampled or otherwise used to regulate theaverage current provided by driver module 300 to LED units 108 a-n.After time period td current I_(SW2) may be sensed and generallydecreases from a value I_(SW2Max) to the minimum current I_(MIN)provided by driver module 104 to the LED units 108 a-n. Accordingly, thecurrents I_(SENSE2) used by regulating module 500 to regulate theoperation of driver module 300 during its “off” state may be expressedmathematically, for any given cycle n, as shown in Equation 2.I _(SENSE2) =Isw2  Equation 2:For any given cycle n, t4 _(n) is the time from when the current sensedby low current sensor 306 is representative of the coil current whilethe low switch 306 is “on”, and t1 _((n+1)) is the time at which the lowswitch 306 is turned “off” and the cycle then repeats.

As shown in FIG. 4C, the “on” and “off” states of the driver module 300may be adjusted such that the I_(MAX) and I_(MIN) values are symmetricalaround the I_(TAR) current and the resulting current I_(LED) provided tothe LED units 108 a-n can be set at the target average current I_(TAR).That is, the average LED current I_(AVG)=I_(TAR) when symmetry exists.Such symmetry may be expressed as the change in current ΔI over a cyclewhere the change ranges from I_(MAX) to I_(MIN). It is to be appreciatedthat ideally, half this change

$\frac{\Delta\; I}{2}$(the current adjustment) arises, respectively, above and below theaverage current I_(AVG) such that symmetry exists. This relationship isexpressed in Equation 3.

$\begin{matrix}{{I_{{MA}\; X} - \frac{\Delta\; I}{2}} = {{I_{M\;{IN}} + \frac{\Delta\; I}{2}} = I_{TAR}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$Per Equation 3, I_(AVG) may be expressed in terms of the peaks (whichare shown in FIG. 4C as the I_(MAX) value at time t3 ^(n)) and valleys(which are shown in FIG. 4C as the I_(MIN) value at time t1 ^((n+1))) ofthe current I_(LED) 400 provided by driver module 300 to the LED units108 a-n. This relationship may also be expressed in terms of such ΔI's,as shown in Equation 4.

$\begin{matrix}{I_{AVG} = {\frac{I_{M\;{AX}} + I_{M\; I\; N}}{2} = {\frac{\left( {I_{TAR} + \frac{\Delta\; I}{2}} \right) + \left( {I_{TAR} - \frac{\Delta\; I}{2}} \right)}{2} = I_{TAR}}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Further, it should be appreciated that when symmetry exists betweenI_(MAX) and I_(MIN), I_(TAR) does not depend on the inductance value Lof coil 122. Likewise, I_(TAR) does not depend on the voltage V_(in)provided, for example, by a power source 102, or on the load (expressedas the output voltage V_(LED)) needed by LED units 108 a-n at any giventime. Further, it should be appreciated that when symmetry existsbetween I_(MAX) and I_(MIN) around I_(TAR), the average LED valueI_(AVG) does not depend at all on ΔI value. It means that ΔI value isfree to be controlled independently to the desired LED value I_(TAR).

Further, it is to be appreciated that the LED current commonly presentsitself, over one cycle to a next, as a constantly varying currentI_(LED) 400 whose boundaries at any given instance in time are definedby I_(MAX), when driver module 300 is “on”, and, by I_(MIN), when drivermodule 300 is “off”.

The “on” and “off” times of driver module 300 can also be expressed interms of the switching frequency

_(n) of the driver module 300, where the frequency

_(n) is inversely proportional to the time length T_(n) of any givencycle n, where the length of any given cycle is the time period T_(n) asshown in Equation 5.

_(n)=1/(t _(ONn) +t _(OFFn))=1/T _(n).  Equation 5:

Accordingly, for at least one embodiment of the present disclosure, theswitching frequency

_(n) can be expressed in terms of a target switching period T_(TAR) fordriver module 300, which can also be expressed in terms of the voltagesand inductance properties of a given driver module, for any given cyclen, as shown in Equation 6.

$\begin{matrix}{{(n)} = {\frac{1}{T} = {\frac{1}{T_{TAR}} \cong \frac{V_{LED} \cdot \left( {V_{I\; N} - V_{LED}} \right)}{\Delta\;{I \cdot L \cdot V_{I\; N}}}}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$In view of these expressions and relationships, and as discussed furtherbelow with reference to FIG. 5, regulating module 500 may control theI_(LED) current at the desired I_(TAR)=I_(AVG) value by adjusting theI_(MAX) and I_(MIN) threshold limits symmetrically above and belowI_(TAR) independently of ΔI value according to Equation 4 as well asregulating module 500 may control the frequency

_(n) of each cycle as well as the timing of when driver module 300switches from the “on” to “off” states within any given cycle byadjusting the ΔI value according to Equation 6.

Referring now to FIG. 5 for at least one embodiment of the presentdisclosure, a regulating module 500 for controlling the switchingfrequency of a driver module 300 as well as the respective “on” and“off” times of such a driver module 300 is shown. The regulating module500 may be coupled to hi lead 308, low lead 310, target input lead 502,hi switch lead 504, and low switch lead 506. It is to be appreciatedthat other leads, such as power, programming, ground, clocking andothers and/or other commonly used components may be utilized, but, arenot shown in FIG. 5.

Regulating module 500 may include a first summing module 508 coupled toeach of the target input lead 502, adjustment lead 510, and max. currentlead 512. First summing module 508 may be configured to sum a targetcurrent signal, I_(TAR), received via lead 502, with a currentadjustment signal ΔI/2, received via lead 510, and output the resultingI_(MAX) current signal via lead 512.

Regulating module 500 may include a second summing module 514 coupled toeach of the target input lead 502, adjustment lead 510, and min. currentlead 516. Second summing module 514 may be configured to sum the targetcurrent signal, I_(TAR), received via lead 502, with the opposite signvalue of the current adjustment signal ΔI/2 received via lead 510, andoutput the resulting I_(MIN) current signal via lead 516. It is to beappreciated, that while shown in the embodiment of FIG. 5 as utilizingtwo summing modules, 508 and 514, such modules may be provided in asingle module where the value of the adjustment signal 510 varies basedon the state (i.e., “on” or “off”) of the driver module 300 at any giventime.

As further shown for at least the embodiment depicted in FIG. 5,regulating module 500 may also be configured to include a frequencyadjustment module 518, which outputs the current adjustment signal ΔI/2.For at least one embodiment, the frequency adjustment module 518 willoutput a stable adjustment signal ΔI/2 within a given number ofpre-determined cycles following initiation of the driver module for afirst cycle at time t1 ¹. In at least one embodiment, the frequencyadjustment module 518 may be replaced by any module adjustingsymmetrically I_(MAX) and I_(MIN) threshold currents versus the targetaverage current I_(TAR) via any regulation technique. Examples of suchregulation techniques include but are not limited to proportional,integral-proportional, derivative-integral-proportional and other knowntechniques.

It is to be appreciated that in accordance with at least one embodimentof the present disclosure, for an ideal implementation, the combinationsof summing modules 508 and 514 and the signal amplitude of currentadjustment signal ΔI/2 may result in I_(AVG) commonly being equal toI_(TAR), with any differences, if any, not effecting the mode ofoperation of the LED units 108 a-n. It is to be appreciated that innon-ideal implementations, pure symmetry may not arise due to, forexample, current losses occurring during switching activities,comparator 534 and 524 delays, delays in sensing elements 314 and 316,errors in summing modules 508 and 514, comparator offsets in 534 and524, delay in pre-drivers 530, 532 or in transistors 304 and 306, delayin control module 528 and the like. Generally, any such differences mayresult in insubstantial decreases in the performance of the LED units108 a-n. Such insubstantial differences arising within known and/orexpected performance ranges for the LED units 108 a-n. Further, it is tobe appreciated that, for an ideal circuit, when I_(AVG)=I_(TAR) the LEDcurrent I_(LED) does not need to be regulated and will instead becorrectly set at the desired current.

In accordance with at least one embodiment of the present disclosure, itis to be appreciated that the effective average current I_(EAVG) may besensed by any state-of-the-art technique not presented here. Theeffective average current I_(EAVG) could be provided to each of thefirst and second summing modules 508 and 514 as a second ordercorrection signal. It is to be appreciated that such a second ordercorrection signal may allow for the apparatus to adjust for errors thatotherwise arise from the use of non-ideal components.

Frequency adjustment module 518 may be operably coupled, via change timeperiod lead 520, to a period compare module 522. As further shown for atleast one embodiment of the present disclosure, the period comparemodule 522 may be configured to determine the state of operation of thedriver module 300 based, for example on detecting when the time periodsignal ΔT occurs. It is to be appreciated that for at least oneembodiment of the present disclosure the period compare module 522 maybe replaced by a module which compares an actual switching period (orfrequency) to a target switching period (or frequency) over multiplecycles. Such a period compare module 522 may be utilized to flush-outpermutations arising under operating conditions where the load demandedby the LED units 108 a-n are rapidly changing, as may be the case, forexample, when strobing, rapidly flashing or similar modes of operationmay be desired. Further, it should be appreciated that the periodcompare module 522 may be implemented in either the analog circuit ordigital circuits and processing domains.

It is to be appreciated that for at least one embodiment, the periodcompare module 522 may compare the total time periods T or a portionthereof, such as t_(ON) or t_(OFF) as arising from one cycle to a next.In one embodiment, only the actual versus target “off” times for thedriver module 300 are compared and for at least one embodimentΔT=Δt_(OFF)=t_(OFF) ^((n))−t_(OFF(n−1)). The inverse of ΔT is thedesired switching frequency for the driver module 300. For at least oneembodiment, the desired switching frequency is, for example, 2 MHz, andthe corresponding target period is 500 ns.

As further shown for at least the embodiment depicted in FIG. 5,regulating module 500 may also be configured to include a low comparatormodule 524 which is coupled to each of the period compare module 522(via “set” lead 526), the second summing module 514 (via min currentlead 516) and to the low current sensor module 316 (via low lead 310).Low comparator module 524 may be configured to monitor when theI_(SENSE2) current signal provided via the low lead 310 is equal to theI_(MIN) threshold provided to the low comparator module 524 by thesecond summing module 514. As discussed previously above, whenI_(SENSE2)=I_(MIN) a new cycle for the driver module 300 occurs.Accordingly, upon detecting I_(SENSE2)=I_(MIN) the low comparator module524 outputs a “set” signal S, which designates the start of t_(ON) and anew (n+1) cycle, to each of the period compare module 522 (via set lead526) and to a driver control module 528.

As further shown for at least the embodiment depicted in FIG. 5, thedriver control module 528 may be configured, upon receiving the setsignal S to initiate the closing of the hi switch 304 and the opening ofthe low switch 306, with the sequence of operation commencing from timeperiods t1 _(n) through t3 _(n), as shown in FIG. 4A, with the “on”state.

As shown for at least one embodiment of the present disclosure, drivercontrol module 528 may be coupled via (optional) high switch module 530and (optional) low switch module 532 to the respective hi switch 304 andlow switch 306, via respective hi switch lead 504 and low switch lead506. It is to be appreciated that the high switch module 530 and lowswitch module 532 are designated as optional components of regulatingmodule 500 as the need for signal condition, including amplification,filtering or otherwise may vary based upon actual implementations of oneor more of the embodiments described herein.

As further shown for at least the embodiment depicted in FIG. 5,regulating module 500 may also be configured to include a hi comparatormodule 534. Hi comparator module 534 may be coupled to each of hicurrent sensor module 314 (via hi lead 308) and to first summing module508 (via max current lead 512). Hi comparator module 534 may beconfigured to monitor when the I_(SENSE1) current signal provided viathe hi lead 308 is equal to the I_(MAX) threshold provided by the firstsumming module 508. As discussed previously above, whenI_(SENSE1)=I_(MAX) the “off” portion of a given cycle n for the drivermodule 300 is deemed to occur. Accordingly, upon detectingI_(SENSE1)=I_(MAX) the hi comparator module 534 outputs a “reset” signalR, which designates the start of t_(OFF) to the driver control module528. It is to be appreciated that in accordance with at least oneembodiment, the period compare module 522, or a second period comparemodule (not shown), may be utilized to provide further refinement of theI_(MAX) currents which, when sensed by hi current sensor 314, initiatethe triggering of the “off” period. That is, it is to be appreciatedthat the hi comparator module 534 may be configured to also communicatethe reset signal R to the period compare module 522, which, in turn,determines whether any difference have occurred between the actualt_(OFF) time and the t_(OFF) target time and, if so, instructs thefrequency adjustment module to output an adjustment signal ΔI/2specifically targeted for increasing (or decreasing) the I_(MAX) currentsignal. That is, it is to be appreciated that for one or moreembodiments, separate adjustment signals ΔI/2 may be output by theadjustment module 518 so as to separately adjust the I_(MAX) and I_(MIN)current signals, as then being adjusted based on the then operatingstate of driver module 300. Such separate adjustments may be desired,for example, when adjustments to only one of the I_(MAX) and I_(MIN)current signals, and not both, is desired so as to provide a moreprecise symmetry of I_(MAX) and I_(MIN) with respect to I_(AVG). It isto be appreciated that such separate adjustment may arise in view of oneor more operational, environmental or other constraints.

Referring now to FIG. 6 and with respect to at least one embodiment ofthe present disclosure, a second regulating module 600 may be providedwhich may be configured for use with a single current sensing module602. Per at least this embodiment, it is to be appreciated that the hicurrent sensor 314 and low current sensor 316, as shown in FIGS. 3 and5, may be augmented and/or replaced by the single current sensing module602. The single current sensing module 602 may desirably be positionedto sense the current across the coil 122 of the buck driver module 104(see FIG. 3) by being positioned, for example, at the junction formed byleads extending from and coupling to each of the other the hi switch304, low switch 306, and coil 122. It is to be appreciated that the coilcurrent is essentially the LED current I_(LED) flowing through thedriver module 300. It is to be appreciated that for any embodiment thelocation of the single current sensing module 602 relative to the drivermodule 304 may vary provided, however, that the current provided to theLED units 108 a-n during both the “on” and “off” states of any givencycle may be sensed. Further, per at least one embodiment, the singlecurrent sensing module 602 may be coupled to the low comparator module524 (FIG. 5), to output thereto the I_(SENSE3) current signal via lead604. It is to be appreciated that the I_(SENSE3) single sensed currentsignal equals I_(LED) during all states and cycles of operation for thedriver circuit 304.

As further shown in FIG. 6 and with respect to at least one embodimentof the present disclosure, the hi comparator module 534 (FIG. 5) and lowcomparator module 524 (FIG. 5) may be replaced by a joint comparatormodule 601 which may be configured to operate with respect to two ormore thresholds, such as the t_(ON) and t_(OFF) thresholds.Additionally, both the I_(MAX) and I_(MIN) current signals may becommunicated by the first summing module 508 and the second summingmodule 514 to a multiplexer 606. The multiplexer 606 may be configuredto communicate the corresponding I_(MIN) or I_(MAX) signal, as dependingon the current state (“on” or “off”) then being sensed by the singlecurrent sensing module 602, to the joint comparator module 602.

As further shown in FIG. 6 with respect to at least one embodiment ofthe present disclosure, the multiplexer 606 may be coupled to the jointcomparator module 601 via lead 608 and the joint comparator module 601may be configured to output the set signal S to multiplexer 606 via lead610. The multiplexer 606 may be configured to toggle between the signalsbeing provided on lead 512 and lead 516 based on the then correspondingstate, “on” or “off” as represented by the set signal, of the drivermodule 300 for that given cycle n.

Although various embodiments of the claimed invention have beendescribed above with a certain degree of particularity, or withreference to one or more individual embodiments, those skilled in theart could make numerous alterations to the disclosed embodiments withoutdeparting from the spirit or scope of the claimed invention. Otherembodiments are therefore contemplated. It is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative only of particularembodiments and not limiting. Changes in detail or structure may be madewithout departing from the basic elements of the invention as defined inthe following claims.

What is claimed is:
 1. A power supply comprising: a buck convertermodule operably connected to a power source and a load; a first switchconfigured to operably couple the power source to the buck convertermodule during a first period of a given operating cycle; wherein duringthe first period the buck converter module stores and provideselectrical power from the power source to the load; wherein theelectrical power provides a current and a voltage to the load; a secondswitch configured to, during a second period of the given operatingcycle, operably discharge to the load the electrical power stored in thebuck converter module during the first period; and a first currentsensor configured to sense the current during at least one of the firstperiod and the second period; wherein, over the operating cycle, thecurrent is maintained at an average current by an adjustment of at leastone of a maximum and a minimum of the current provided to the loadduring the given operating cycle.
 2. The power supply of claim 1,wherein operating states for the first switch and the second switch aresubstantially diametrically opposed.
 3. The power supply of claim 1,wherein adjustments to the first period adjust the maximum of thecurrent provided to the load during the given operating cycle; andwherein adjustments to the second period adjust the minimum of thecurrent provided to the load during the given operating cycle.
 4. Thepower supply of claim 3, wherein the first period is adjusted based upona comparison of a desired maximum current and a present value of thecurrent provided to the load during the given operating cycle; whereinthe second period is adjusted based upon a comparison of a desiredminimum current and a present value of the current provided to the loadduring the given operating cycle.
 5. The power supply of claim 4,wherein the first current sensor is configured to sense the currentduring each of the first period and the second period at a junctionelectrically coupling each of the first switch, the second switch andthe buck converter module.
 6. The power supply of claim 4, comprising: asecond current sensor configured to sense the current during the secondperiod; wherein the first current sensor is configured to sense thecurrent during the first period.
 7. The power supply of claim 4,comprising: a regulating module, operably coupled to the first switch,the second switch and the first current sensor, and configured to:instruct the first switch to open and the second switch to close whenthe current equals a desired maximum current during the given operatingcycle; and instruct the first switch to close and the second switch toopen when the current equals a desired minimum current during the givenoperating cycle; wherein upon closure of the first switch and opening ofthe second switch a next operating cycle begins.
 8. The apparatus ofclaim 7, wherein the average current is a target current for the loadfor the given operating cycle.
 9. An apparatus for regulating theoperation of a power supply module, comprising: a first comparator,coupled to a low current sensor, configured to detect when a minimumcurrent provided by a power supply module to a load reaches a targetminimum current and, when such detection occurs, output a set signal;and a second comparator, coupled to a high current sensor, configured todetect when a maximum current provided by the power supply module to theload reaches a target maximum current, and when such detection occurs,output a reset signal; a driver control module, coupled to the firstcomparator, the second comparator, a high switch, and a low switch, andconfigured to control operating states of each of the low switch and thehigh switch in response to receipt of the set signal and the resetsignal; whereupon receipt of the reset signal, the low switch is closed,the high switch is opened, and the power supply module enters a secondperiod of a current operating cycle having a first period followed bythe second period, wherein electrical power stored in the power supplymodule is discharged to the load at an output current and an outputvoltage; and whereupon receipt of the reset signal, the low switch isopened, the high switch is closed, and the power supply module entersthe first period of the current operating cycle, wherein electricalpower provided by a power source is stored in the power supply moduleand provided by the power supply module to the load as the outputcurrent and the output voltage.
 10. The apparatus of claim 9, whereinthe output current is regulated to a desired target current over theoperating cycle by adjusting at least one of the target maximum currentand the target minimum current.
 11. The apparatus of claim 10,comprising: a period compare module, coupled to at least one of thefirst comparator and the second comparator, configured to: measure forthe current operating cycle at least one of a minimum time and a maximumtime; wherein the minimum time arises during the second period and isthe amount of time needed for the output current to decrease from amaximum current to the target minimum current; and wherein the maximumtime arises during the first period and is the amount of time needed forthe output current to increase from a minimum current to the targetmaximum current; compare the minimum time measurement for the currentoperating cycle with a previous minimum time measurement for a previousoperating cycle; and output a result of the comparison.
 12. Theapparatus of claim 11, comprising: an adjustment module, coupled toreceive the output of the period compare module, and configured to:receive the output of the period compare module; determine a switchingfrequency of the driver module; compare the switching frequency of thecurrent operating cycle to a target switching frequency; and outputbased on a result of such comparison a current adjustment signal. 13.The apparatus of claim 12, wherein the current adjustment signal isutilized to adjust at least one of the target minimum current providedto the first comparator and the target maximum current provided to thesecond comparator.
 14. The apparatus of claim 13, wherein the currentadjustment signal indicates an amount of change desired in the currentto be provided to the load during the next cycle.
 15. The apparatus ofclaim 14, wherein the power supply module comprises a buck converter.16. The apparatus of claim 11, comprising an adjustment moduleconfigured to symmetrically adjust the target maximum current and thetarget minimum current based upon the output from the period comparemodule for the current operating cycle for use with an immediatelysubsequent operating cycle.
 17. A method for regulating a power supply,comprising: adjusting an “on-time” period for a power supply module suchthat an output current of the power supply module does not exceed atarget maximum current for the power supply module; and adjusting an“off-time” period for the power supply module such that an outputcurrent of the power supply module does not exceed a target minimumcurrent for the power supply module; wherein an operating cycle for thepower supply module includes the “on-time” period and the “off-time”period; wherein the target maximum current and the target minimumcurrent are set such that the output current of the power supply equalsa target output current over the operating cycle.
 18. The method ofclaim 17, wherein the target maximum current and the target minimumcurrent are symmetrically disposed about an average output current equalto the target output current.
 19. The method of claim 18, comprising:wherein adjusting the “on-time” period and the “off-time” periodcomprises: comparing the output current of the power supply module forthe current operating cycle to each of the target maximum current andthe target minimum current; when the output current equals the targetminimum current; configuring a first switch into a first operatingstate; configuring a second switch into a second operating state;providing the target maximum current for use in the comparing operation;when the output current equals the target maximum current; configuringthe first switch into the second operating state; configuring the secondswitch into the first operating state; and providing the target minimumcurrent for use in the comparing operation.
 20. The method of claim 19,comprising: receiving the target output current; during the “on-time”period, determining the target maximum current by adding an adjustmentsignal to the target output current; during the “off-time” period,determining the target minimum current by subtracting the adjustmentsignal from the target output current; wherein the adjustment signalrepresents a change in the target maximum current or target minimumcurrent desired for the output current for the next operating cycle toequal the target output current; wherein the adjustment signalrepresents an inverse of the respective difference arising between afirst duration for a previous operating cycle and second durationutilized for the current operating cycle; and wherein during the firstduration and second durations are determined for each “on-time” periodand each “off-time” period.